In a manufacturing process of a semiconductor device or an FPD (flat panel display), a plasma is often used in processes, e.g., etching, deposition, oxidation, sputtering and the like, in order to allow a processing gas to react efficiently at a relatively low temperature. Conventionally, a capacitively coupled plasma processing apparatus capable of producing a large-diameter plasma has been mainly used for a single-wafer plasma processing apparatus.
Generally, in the capacitively coupled plasma processing apparatus, an upper and a lower electrode are disposed in parallel with each other in a vacuum processing chamber, and a substrate to be processed (e.g., a semiconductor wafer, a glass substrate or the like) is mounted on the lower electrode. When a high frequency is applied to one of the electrodes, electrons accelerated by a high frequency electric field between the electrodes, secondary electrons emitted from the electrodes, and heated electrons collide with molecules of a processing gas. Accordingly, a plasma of the processing gas is generated, and a required microprocessing, e.g., etching, is performed on a substrate surface by radicals or ions in the plasma. In the etching process, there is widely used a dual frequency application mode in which a relatively high frequency (normally higher than or equal to about 40 MHz) for plasma generation (discharge) is applied to any one of the upper and the lower electrode and a relatively low frequency (lower than or equal to about 13.56 MHz) for ion attraction to the substrate is applied to the lower electrode.
Japanese Patent Laid-open Publication No. 2006-270019 discloses a type of the capacitively coupled plasma processing apparatus in which a plasma is generated between two electrodes by a high frequency discharge while a DC voltage is applied to an upper electrode facing a substrate via the plasma (hereinafter, referred to as a “DC voltage application type”). In the DC voltage application type, at least one of following effects (basic effects) can be obtained: (1) sputtering effect (deposit removal effect) on the upper electrode is enhanced by increasing an absolute value of a self-bias voltage of the upper electrode; (2) the generation amount of plasma is reduced by enlarging a plasma sheath with respect to the upper electrode; (3) electrons generated near the upper electrode are irradiated onto a substrate to be processed; (4) a plasma potential can be controlled; (5) electron density (plasma density) is increased; and (6) the plasma density in the central portion is increased. Based on the above basic effects, plasma ignition stability, resist selectivity, etching rate and etching uniformity (process characteristic effects) are improved in the etching process.
In the capacitively coupled plasma processing apparatus employing the above DC voltage application type, when a DC voltage is applied to the upper electrode, electrons are accumulated on the upper electrode, which may cause an abnormal discharge between the inner wall of the chamber and the upper electrode. To that end, a DC ground electrode referred to as a DC ground part or a DC block is provided on, e.g., the inner wall of the chamber. The DC ground part is a conductive member made of, e.g., Si, SiC or the like, and is installed at a portion exposed to the plasma on the inner wall of the chamber. The electrons accumulated on the upper electrode pass through the plasma to reach the DC ground part, and then flow to a ground line via the inner wall of the chamber.
However, when deposits such as polymer and the like generated during the etching process are adhered to the surface of the DC ground part, the DC ground function deteriorates and, further, the basic effects of the DC voltage application type or the process characteristic effects decrease.
Conventionally, in order to prevent or reduce the adhesion of deposits to the DC ground part, the DC ground part, which has been connected to the ground line during the etching processing, is supplied with a negative DC voltage when performing cleaning of the DC ground part (plasma cleaning). As a result, a plasma sheath near the DC ground part is made to be enlarged and bombardments of ions accelerated by an average electric field of the plasma sheath to the DC ground part are strengthened to thereby enhance ion sputtering effect and remove the deposits from the surface of the DC ground part.
However, the method for cleaning the DC ground part is disadvantageous in that the cleaning process is required in addition to the etching process, and thus the production efficiency decreases. Besides, in order to improve the cleaning efficiency of the cleaning technique using the sputtering of ions accelerated by the average electric field of the plasma sheath, the DC bias applied to the DC ground part needs to be markedly increased, and an installation cost of the DC power supply or a manufacturing cost of the high pressure power supply line increases.